Field of the Invention
The present invention relates to a technique of transmitting or receiving video data through wireless communication using a directional antenna.
Description of Related Art
In the related art, when a video receiving terminal selects and displays videos transmitted from a plurality of video transmitting terminals, a video signal switching device (a switcher) is arranged between the video receiving terminal and the video transmitting terminals, the video receiving terminal is connected with the video signal switching device using a cable, the video signal switching device is connected with the video transmitting terminals using a cable, and the video signal switching device is controlled such that selection of a video is performed. When the number of video receiving terminals to be used and the number of video transmitting terminals to be used are increased, there is a problem in that cable wiring and a configuration of the video signal switching device become complicated, and it is hard to promptly cope with a change in the layouts of the video receiving terminal and the video transmitting terminal.
In recent years, as a wireless transmission technique has been improved, it has become possible to wirelessly transmit high-definition video from a video transmitting terminal to a video receiving terminal, and a method of selecting a video to be displayed on the video receiving terminal by switching a wireless connection between the video receiving terminal and the video transmitting terminal has been considered.
As a wireless transmission technique of video data, a millimeter wave radio technique using a 60 GHz band capable of using a broad bandwidth and performing high-speed wireless transmission has attracted attention (for example, see Japanese Unexamined Patent Application, First Publication No. 2011-82876). In a wireless HD standard that is a standard of a millimeter wave radio technique, a high rate PHY (HRP) that is a high-speed transmission channel and a low rate PHY (LRP) that is a low-speed transmission channel are specified.
The HRP is limited in a range of a communication path since a narrow-directional antenna is used, but since a high gain is obtained, the HRP is used for high-rate video data transmission such as transmission of video data. However, the LRP is less limited in a range of a communication path than the HRP since a wide-directional antenna is used at a low rate, and since communication is hardly interrupted, the LRP is used for transmission of control data or the like.
A wireless millimeter wave has a property of being close to light and has a feature of traveling in a straight line, and thus when a shielding object such as a human crosses a communication path, communication is easily interrupted. In order to avoid this problem, for example, when an obstacle moves onto a communication path during transmission of video data and thus a wireless environment gets worse, control for maintaining a communication rate is performed by changing directivity of an antenna using an active array antenna or the like and setting a communication path having a good wireless environment.
For example, as illustrated in FIG. 22, when a communication failure occurs in a communication path P1 while a video transmitting terminal TX is transmitting video data to a video receiving terminal RX using the communication path P1, directivity of an antenna is changed, so that a communication path is changed from the communication path P1 to a communication path P2. However, when a wireless environment changes in a bursting manner due to influence of door opening and closing or the like, it takes time to set an optimal communication path, and a video may be interrupted as illustrated in FIG. 23. FIG. 23 illustrates an example in which video data is transmitted from a video transmitting terminal to a video receiving terminal. Time flows to the right in FIG. 23.
In the example of FIG. 23, a communication path is changed to a communication path P2 after video data of a first frame is transmitted through a communication path P1, but it takes time to change a communication path. There are cases in which video data of a frame to be transmitted is not transmitted in the process of changing a communication path, and thus a video is interrupted.